A touch sensing apparatus is used to detect the touch of a user's finger or other object and convert it into an electrical signal suitable thereto for providing the same, and is applied to various electronic devices for employing it as an input device. For example, the touch sensing apparatus is applied to laptop computer for an input means, in place of a mouse, for controlling the movement of a cursor, or is coupled to a display device for an input means to directly select and implement an icon or menu displayed on a screen of the display device. In addition, the touch sensing apparatus is also used as means for substituting for a button. In recent years, with the trend of large screen and small size in electronic devices, it is increasingly often the case that an input device, such as a keypad, is omitted but a touch input device (e.g., a touch screen) coupled to the display is used as a sole input means (or at least a main input means).
Expansion of application of such a touch sensing apparatus accompanies a change in input schemes, one example of which is a method of sensing two or more touch inputs. A conventional touch sensing apparatus detects only single touch input and also receives restricted inputs. For example, a touch sensing apparatus substituted for a mouse merely controls the position of a cursor through a touch input, and has to use a separate button for an input produced by a click. However, latest touch sensing apparatuses are able to simultaneously detect two or more touch inputs, one for controlling the position of a cursor and the other one for performing a click input. Further, a rotation command to rotate a subject on a screen is implemented by using one input established as a reference and the movement of another input, and an expanding or contracting command for a subject on a screen is also implemented depending on a change in the distance between two inputs.
In order to detect two or more touch inputs, the existence of two or more touch inputs has to be determined first, which is known from a prior art such as a method based on the maximum and minimum values of a signal generated by two inputs. For instance, U.S. Pat. No. 5,825,352 discloses a method of measuring two maxima and minima between the maxima and determining the existence of two or more touch inputs based on the maxima and minima.
However, it is difficult to apply the method of using the maxima and minima if two inputs are adjacent to each other. For example, if two touches are close, the minima between the maxima may have a greater value than expected one because signals caused by such touches overlap with each other and, therefore, it becomes very difficult to set a threshold value for discriminating the signals from noises and sensing the touches as two-touch input. Therefore, in order to detect adjacent touch inputs by the method using maxima and minima, sensing electrodes for sensing touches need to be densely disposed to increase the resolution. However, this measurement causes an increase of manufacturing costs, which results in a complicated routing between electrodes and circuits, and thus makes it difficult to manufacture small-sized devices. Particularly, for a touch screen, which is one of touch sensing apparatuses, such complicated routing typically increases the area of a wiring portion disposed on the outer periphery (so-called bezel) of a display device, thereby hindering the expansion of the screen.